The fabrication of microelectronic integrated circuitry generally involves the patterning of device structures and layouts on a semiconductor substrate. The accepted practice for creating the requisite pattern is to first form a replica of the pattern on a mask (not necessarily in its final size) and then to transfer the mask pattern to a layer of photoresistive material, either positive or negative photoresist, formed on the semiconductor substrate. The transfer is accomplished by an optical photolithographic process, shining light of a certain wavelength through the mask and onto the photoresist, using whatever optical lenses are required to replicate the pattern in its proper size on the photoresist. Once the pattern has been transferred to the photoresist, the photoresist is processed to selectively remove portions of the pattern and expose the substrate below. The substrate itself can then be etched by, for example, an anisotropic plasma etch, wet etch, or otherwise processed as required.
With the progressive shrinking of device sizes to as small as tenths of a micron or below, the dimensions of patterns to be transferred by optical photolithography are approaching the sub-wavelengths of the optical radiation. As this occurs, maintaining both a high pattern resolution and a depth of focus to allow good patterning on a substrate of imperfect planarity may become a problem.
Accordingly, what is needed is a system and method of using interferometric photolithography that is simple and/or applicable to a wider range of patterns.